This invention relates to a foam control composition for use in aqueous foaming systems. More particularly, this invention relates to a composition comprising a mixture of a silicone defoamer reaction product and a silicone glycol which is especially useful in controlling foam in highly acidic or highly basic systems operating at elevated temperatures.
The use of various silicone containing compositions as antifoams or defoamers is known. In this regard, it is well established that this art is highly unpredictable and slight modification can greatly alter performance of such compositions. Most of these compositions contain silicone fluid (usually dimethylpolysiloxane), often in combination with small amounts of silica filler. Additionally, these compositions may include various surfactants and dispersing agents in order to impart improved foam control or stability properties to the compositions.
Thus, for example, Rosen, in U.S. Pat. No. 4,076,648, teaches self-dispersible antifoam compositions consisting essentially of a lipophilic nonionic surface active agent homogeneously dispersed in a non-emulsified diorganopolysiloxane antifoam agent. This combination is said to promote dispersibility in water without the need for emulsification.
Kulkarni et al., in U.S. Pat. No. 4,395,352, improved upon the compositions disclosed by Rosen, cited supra, by limiting the viscosity of the dimethylpolysiloxane oil therein to the range of 5,000 to 30,000 cS at 25.degree. C. Such a limitation, it is taught, unexpectedly resulted in improved efficiency in difficult-to-defoam aqueous systems, such as those which contain high concentrations of ionic surfactants and those which are very viscous.
Keil, in U.S. Pat. No. 3,784,479, discloses foam control compositions which consist essentially of a base oil selected from polyoxypropylene polymers, polyoxypropylenepolyoxyethylene copolymers or siloxane-glycol copolymers, a foam control agent, comprising a liquid dimethylpolysiloxane and silica filler, and a dispersing agent which consists of a copolymer of a siloxane resin and a polyoxyalkylene polymer. The contribution to the art in this case is stated to be improved compatibility with otherwise desirable diluents without resorting to emulsifying the foam control agent in water.
In a closely related patent, U.S. Pat. No. 3,984,347, Keil discloses foam control compositions which consist essentially of a base oil selected from polyoxypropylene polymers, polyoxypropylene-polyoxyethylene copolymers or siloxane-glycol copolymers, a foam control agent comprising a liquid dimethylpolysiloxane and silica filler and a siloxane copolymer dispersing agent. This time the dispersing agent consists of a copolymer of a dimethylpolysiloxane polymer and a polyoxyalkylene polymer. The same advantages as reported for U.S. Pat. No. 3,784,479, cited supra, were obtained.
A composition suitable for use as a defoamer in dyeing operations is taught by Colquhoun in U.S. Pat. No. 3,912,652. In this case, the composition consists of a copolymer of a dimethylpolysiloxane polymer and a polyoxyalkylene polymer combined with a lesser amount of a copolymer of a siloxane resin and a polyoxyalkylene polymer. Such compositions are stated to be particularly useful in jet dyeing operations since they are compatible with the dye carriers employed therein.
Japanese O.P.I. No. 139,107/81, published Oct. 30, 1981, teaches a self-emulsifying type defoaming agent which is said to have excellent foam-suppressing and breaking capability regardless of temperature and pH of a liquid to be treated and the storage period to which it is subjected. This agent is composed of a silicone copolymer having diorganosiloxane and organo-oxyalkylenesiloxane units in the copolymer chain.
A process for control of foaming in non-aqueous systems is disclosed by Lomas in U.S. Pat. No. 4,460,493. The compositions employed consist essentially of (1) at least one foam control agent, selected from polydimethylsiloxane or poly(methyl-3,3,3-trifluoropropyl)siloxane, which may optionally include a minor portion of a siloxane resin, (2) a dispersing agent of the type described in the patents to Keil, cited supra, and (3) a non-ionic surfactant having an HLB number greater than 10. This invention is said to provide an effective and cost efficient foam control method for the non-aqueous systems described. A similar composition containing a high molecular weight polydimethylsiloxane was also shown to be useful in defoaming highly acidic aqueous systems by Schiefer in copending application Ser. No. 940,686, filed Dec. 11, 1986, now U.S. Pat. No. 4,762,640.
Aizawa et al., in U.S. Pat. No. 4,639,489 and copending application Ser. No. 930,611 filed on Nov. 14, 1986, now U.S. Pat. No. 4,749,740, the disclosures of which are hereby incorporated by reference, teach a method for producing a silicone defoamer composition wherein a complex mixture of polyorganosiloxanes, filler, a resinous siloxane and a catalyst to promote reaction of the other components are heated together at 50.degree. C. to 300.degree. C.
More recently, a method for preparing a composition similar to that described by Aizawa et al., cited supra, was disclosed in Australian Patent Application No. 75771/87, published on Jan. 21, 1988 and assigned to Dow Corning KK. In this disclosure, the abovementioned complex silicone mixture additionally contains at least 0.2 weight parts of an organic compound having at least one group selected from .ident.COR, --COOR' or --(OR").sub.n --, wherein R and R' are hydrogen or a monovalent hydrocarbon group, R" is a divalent hydrocarbon group having 2 to 6 carbon atoms and the average value of n is greater than one. In this disclosure the inventor, T. Miura, emphasizes the need to react all the ingredients, including a catalyst, at elevated temperature to obtain the desired antifoam agent.